Misfit dislocations often arise when a second thin film layer is deposited on a first thin film layer. This is particularly true in instances where the first and second thin film layers have different in-plane lattice parameters. In such instances, initial growth of the second thin film layer may be commensurate to the in-plane lattice parameters of the first layer. As growth of the second thin film layer continues, misfit strain may build within the second thin film layer due to the difference in lattice parameters between the first and second layers. Eventually, misfit or other dislocations will arise in the second thin film layer to relieve this strain. The thickness at which misfit dislocations arise in a thin film layer is known in the art as the “critical thickness.”
With the foregoing in mind, thin film technology is often used to produce optoelectronic devices such as light emitting diodes. For example, some LEDs may be formed from a plurality of thin film layers that are deposited on a substrate. Due to differences in the lattice parameters of the substrate and the layers grown thereon (or between subsequent successive layers), misfit dislocations may arise. Such dislocations can reduce the optical efficacy of the LED, and may increase the electrical resistance of n and p type semiconductive layers/regions used therein. This is particularly problematic in the case of LEDs that include active regions designed to emit ultraviolet light, wherein misfit dislocations may play a significant role as non-radiative recombination centers.